This invention relates to an apparatus and a method for image processing. More specifically, the invention relates to an apparatus and a method for image processing in which an image having a strong possibility of failing in computing a proper amount of image correction in an image correcting amount computing unit, such as an image belonging to a group that contains images taken with unusual types of light sources and images having a color failure, or a group that contains images taken with backlight and images taken with an electronic flash is subjected to an operator's judgment.
Heretofore, images recorded on photographic films such as negative and reversal films (which are hereunder referred to simply as “films”) have been commonly printed on light-sensitive materials (photographic papers) by means of direct (analog) exposure in which the film images are projected onto the light-sensitive materials to achieve their areal exposure.
A new technology has recently been introduced and this is a printer that relies upon digital exposure. Briefly, an image recorded on a film is read photoelectrically, converted to digital signals and subjected to various image processing steps to produce image data for recording purposes; recording light that has been modulated in accordance with the image data is used to scan and expose a light-sensitive material to record a latent image, which is subsequently developed to produce a finished print (photograph). The printer operating on this principle has been commercialized as a digital photoprinter.
In the digital photoprinter, the image is converted to digital image data which is processed to determine exposing conditions for printing. Hence, the digital photoprinter is capable of performing effective image processing operations such as the correction of washed-out highlights or flat shadows due to photography with backlight or an electronic flash, sharpening and the correction of color or density failure and this enables the production of high-quality prints that have been impossible to attain by the conventional direct exposure technique. What is more, by image data processing, a plurality of images can be assembled into one composite image or a single image can be divided into more than one image and even characters can be assembled; thus, prints can be output after editing/processing is done in accordance with a specific use.
Outputting images as prints is not the sole capability of the digital photoprinter; the image data can be supplied into a computer or the like and stored in recording media such as a floppy disk; hence, the image data can be put to various non-photographic uses.
Having these features, the digital photoprinter is basically composed of an image input machine having a scanner (image reading apparatus) that reads an image on a film photoelectrically and an image processing apparatus that processes the image read with the scanner to produce output image data (exposing conditions) as well as an image output machine having a printer (image recording apparatus) that scan exposes a light-sensitive material in accordance with the image data output from the image input machine to record a latent image and a light-sensitive material processor (developing apparatus) that performs development and other necessary processing on the exposed material to produce a print.
In the scanner, reading light issuing from a light source is allowed to be incident on the film, from which projected light bearing the image recorded on the film is produced and focused by an imaging lens to form a sharp image on an image sensor such as a CCD sensor; the image is then read by photoelectric conversion and sent to the image processing apparatus as image data of the image on the film (i.e., image data signals) after being optionally subjected to various image processing steps.
In the image processing apparatus, image processing conditions are set on the basis of the image data read with the scanner and image processing as determined by the thus set conditions is performed on the read image data and the resulting output image data for image recording (i.e., exposing conditions) are sent to the printer.
In the printer, if it is of a type that relies upon exposure by scanning with an optical beam, the latter is modulated in accordance with the image data sent from the image processing apparatus and deflected in a main scanning direction as the light-sensitive material is transported in an auxiliary scanning direction perpendicular to the main scanning direction, whereby a latent image is formed as the result of exposure (printing) of the light-sensitive material with the image bearing optical beam. Development and other processing as determined by the light-sensitive material are then performed in the processor to produce a print reproducing the image that was recorded on the film.
It is empirically known that the transmittances of three colors R, G and B are approximately equal to each other for an image recorded on a correctly exposed film, and that an approximately correct print is obtained by performing image correction so that the average value thereof is approximately equal to a specified value (Evans' principle).
However, scenes taken under unusual types of light sources including a fluorescent lamp and a tungsten lamp, or color failure scenes in which highly saturated colors occupy a large area in the background such as lawn, blue sky or sea do not meet the assumption of the transmittances of three colors R, G and B as mentioned above. Further, in the scene taken with backlight or an electronic flash, the luminance is significantly different between the principle subject and the background. Therefore, the approximately correct print cannot be obtained by the corrective control of the image based on the average value.
To solve this problem, various methods have been proposed to identify these scenes by analyzing the images recorded on a film. However, the conventional methods have not so far attained complete identification of these scenes.
Also in the photoprinter having the layout and functions as mentioned above, image processing function was primarily improved, which enabled production of preferable prints by performing effective correction for most of images on a film. For the particular images as mentioned above however, output prints obtained were often based on erroneous image processing.
Film images that may be subjected to the erroneous image processing in the digital photoprinter include those taken under unusual types of light sources including the above-mentioned fluorescent lamp and tungsten lamp, which are erroneously identified as those having color failure. Both the images have extremely deviated color balance, hence the identification thereof is difficult. The erroneous identification leads to the reversion of the direction in which the correction is performed.
Another example is an image taken with backlight, which is erroneously identified as an image taken with an electronic flash. Extremely high contrast is the feature of both the images. In this case, erroneous identification also leads to the reversion of the direction in which the correction is performed.